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Reverse Modeling of Data Semantics of a VSAM File based Information System

Ulrike Kölsch
Forschungszentrum Informatik, University of Karlsruhe



Poster Abstract

1.0 Problems Identified in VSAM based Legacy Systems

Actually, most information systems (IS) have to deal with problems such as European currency or millennium adaptations. For the long-living legacy systems among them the necessary adaptations are even more difficult because they require changes in the data semantics and structure. The problems arising are based on the fact that applications of file based legacy systems do not only use but also interpret the data. Thus the data semantics is spread over the whole system so that an homogenous and parallel change of all applications and data structures concerned is required. First of all the deduction of an integrated model of the data semantics is needed in order to be able to plan a adaptation process.

2.0 Deducing Data Semantics by Reverse Modelling an Object Model Based on Data and Program Information

To regain a complete and integrated model of the data semantics of an legacy IS it is necessary to use a combined approach of data and program reverse engineering techniques in order to achieve a complete and correct result. The example IS we examine bases on VSAM data files and uses the 3GL PL/I as application programming language. Our major goal is to improve the system structure by re-organizing the application source code using the object-oriented concepts like encapsulation and clearly defined method interfaces. Therefore we use the object-oriented modelling technique OMT as description basis and gather the results obtained in a reverse created object diagram. We use the methods listed below to examine the application programs and the data description sets of the IS. The methods are used explicitly to extract information that detect semantic units as object-like entities to build an object-oriented model of the data. The methods and the achievable results are listed below:

3.0 Conclusions

The deadlock situation in changing either data formats or programs in legacy system is a severe drawback in re-engineering these IS. By deducing the object model of a legacy system this problem is solved because a complete overview of the semantics buried in the stored data and in the interpretation sequences of the programs is provided. Consequently an adaptation path can be search and performed without endangering the existing data basis or the running applications by uncontrolled and unplanned changes of the underlying semantics.

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